An arm of the western
Pacific Ocean, east of the Korean
peninsula, west of
Karafuto (what the Russians call
Sakhalin) and
Honshu,
Japan, north of
East China Sea, south of the
Sea of Okhotsk.
Korea calls it "East Sea".
China,
Japan, and
Russia calls it "Sea of Japan".
Further adding to the confusion, China refers to
East China Sea as "East Sea".
I didn't know Korea was requesting other countries to call the sea as "East Sea," or what they call the "correct" name. However, the problem with
Korea's victim-of-imperialism argument (see below w/u) is that the name "Sea of Japan" became
de facto in the first half of the 19th century, prior to Japanese expansionism in the first half of the 20th century. The name "East Sea" is just that, a name. I see no reason why other countries should change what they call the sea.
Argument for "Japan Sea" :
http://www1.kaiho.mlit.go.jp/KIKAKU/nihonkai/index_eng.htm
Argument for "East Sea" :
http://www.korea.net/issue/eastsea/main.html